Das Caldeiras Research Articles

The Challenging Nature of Volcanic Heritage: The Fogo Island (Cabo Verde, W Africa)

Many volcanic landscapes reflect the essence of volcanism and are particularly attractive to different kinds of visitors, featuring the concept of volcanic geoheritage. The expressiveness of volcanic processes is exacerbated in active volcanoes, which increasingly attracts geotourism, despite the natural hazards associated to such geological environment. This work reports how the 2014–2015 eruption of the Fogo volcano at Cabo Verde (West Africa) affected the geoheritage of the central part of the caldera, classified since 2003 as Natural Park, and which caused the destruction of several villages but enabled the occurrence of new geosites. Chã das Caldeiras is the only inhabited area within the perimeter of the park and the unique case of human settlement inside the crater of an active volcano. Besides agriculture, geotourism is an important economic activity for the local communities, and both were devastated after the eruption. However, after the 2014–2015 crisis and despite the eruption risk the local population decided to return to the affected villages and re-start their former life, including geotourism which has since recorded enormous growth. The volcanic geoheritage has dynamic nature that stand out from the majority of stable geosites, with periodic destruction of geosites and corresponding geotouristic infrastructures, and the emergence of new geosites. But despite the costs of rehabilitating, this type of geoheritage must be seen as an economic asset capable of attracting visitors to travel to destinations subject to the risk of eruptions, therefore contributing to foster the typical community-based tourism of normally inhospitable territories.

Raman-IR spectroscopic, and XRD analysis of selected samples from Fogo Island, Cabo Verde: Implications for ancient Martian volcanology

Several space missions from NASA, and ESA have visited and will land on Mars in the search for life. The last mission to arrive was the Mars 2020 Perseverance rover on 18 February 2021. The next mission to Mars will be ExoMars Rosalind Franklin rover, expected to touch down sometime after 2028. Both Mars2020 and ExoMars are equipped with Raman spectroscopic systems: SuperCam and SHERLOC on Perseverance, and Raman Laser Spectrometer (RLS) on Rosalind Franklin (RF). These instruments will be tasked with identifying rocks, minerals, and potential organic biosignatures on the Martian surface. There are many challenges associated with the qualitative and quantitative analysis of resulting data received from current missions on Mars. It is our belief that studies of new terrestrial Martian analogues can help to overcome these challenges. Here, we introduce Chã das Caldeiras Outcrop, Fogo Island, Cabo Verde as a new volcanic terrestrial analog for Mars. We sampled several areas of relevance in Chã das Caldeiras and conducted a complete band analysis of Raman spectra for targets from this site. Additional analyses included ATR-FTIR and XRD. We detected several pyroxene types (augite and diopside) and plagioclase feldspar species (orthoclase, bytownite, sanidine, albite, and anorthite), olivine (forsterite), oxides (magnetite), and leucite. The alteration and secondary minerals detected were carbonates (calcite and dolomite), oxides (goethite, anatase, and hematite), spinel (chromite), phosphate (apatite), various clays, and zeolites (chabazite and muscovite and analcime). We present the Chã das Caldeiras site as a possible new volcanic analogue for Mars given: 1) the similarities to other volcanic places in the Canary Islands; 2) the exclusive geological evolution that is only present in the volcanic emplacement from the Macaronecia-group; 3) the pristine quality of the samples from the outcrop as well as the alteration volcanic minerals.

UAV-based very high resolution point cloud, digital surface model and orthomosaic of the Chã das Caldeiras lava fields (Fogo, Cabo Verde)

Abstract. Fogo in the Cabo Verde archipelago off western Africa is one of the most prominent and active ocean island volcanoes on Earth, posing an important hazard both to local populations and at a regional level. The last eruption took place between 23 November 2014 and 8 February 2015 in the Chã das Caldeiras area at an elevation close to 1800 ma.s.l. The eruptive episode gave origin to extensive lava flows that almost fully destroyed the settlements of Bangaeira, Portela and Ilhéu de Losna. During December 2016 a survey of the Chã das Caldeiras area was conducted using a fixed-wing unmanned aerial vehicle (UAV) and real-time kinematic (RTK) global navigation satellite system (GNSS), with the objective of improving the terrain models and visible imagery derived from satellite platforms, from metric to decimetric resolution and accuracy. The main result is a very high resolution and quality 3D point cloud with a root mean square error of 0.08 m in X, 0.11 m in Y and 0.12 m in Z, which fully covers the most recent lava flows. The survey comprises an area of 23.9 km2 and used 2909 calibrated images with an average ground sampling distance of 7.2 cm. The dense point cloud, digital surface models and orthomosaics with 25 and 10 cm resolutions, a 50 cm spaced elevation contour shapefile, and a 3D texture mesh, as well as the full aerial survey dataset are provided. The delineation of the 2014/15 lava flows covers an area of 4.53 km2, which is smaller but more accurate than the previous estimates from 4.8 to 4.97 km2. The difference in the calculated area, when compared to previously reported values, is due to a more detailed mapping of the flow geometry and to the exclusion of the areas corresponding to kīpukas (outcrops surrounded by lava flows). Our study provides a very high resolution dataset of the areas affected by Fogo's latest eruption and is a case study supporting the advantageous use of UAV aerial photography surveys in disaster-prone areas. This dataset provides accurate baseline data for future eruptions, allowing for different applications in Earth system sciences, such as hydrology, ecology and spatial modelling, as well as to planning. The dataset is available for download at https://doi.org/10.5281/zenodo.4718520 (Vieira et al., 2021).

A construção dos novos estabelecimentos da Reforma Pombalina da Universidade de Coimbra, dirigida por Guilherme Elsden

Há cerca de três anos, iniciámos um processo de cotejo sistemático da documentação escrita relativa à Reforma Pombalina da Universidade de Coimbra (1772-1777), com os levantamentos, desenhos e projetos para os novos estabelecimentos, dirigidos e produzidos pelo Tenente-Coronel de origem britânica Guilherme Elsden. Nesse quadro, realizámos uma comunicação para o ciclo de conferências «A Universidade de Coimbra no caminho para a Contemporaneidade», da 19ª Semana Cultural da Universidade de Coimbra (dedicada ao tema «Quem somos?»), que teve lugar na Casa das Caldeiras, em Coimbra, a 27 de abril de 2017. Coordenámos, seguidamente, uma exposição de desenhos da Reforma Pombalina, no Museu Nacional de Machado de Castro (com a Dr.ª Virgínia Gomes, patente entre outubro de 2018 e fevereiro de 2019), onde pudemos organizar cronologicamente um conjunto alargado de peças gráfi cas (algumas pertencentes à Biblioteca Geral da Universidade de Coimbra), sequência que veio validar e reforçar a nossa primeira leitura dos factos. No presente artigo (que resulta, em grande medida, do texto da comunicação de 2017) retomamos o estabelecimento de uma base cronológica para a datação de alguns desenhos-chave que foram sendo realizados no curto espaço de pouco mais de um ano, entre finais de 1772 e inícios de 1774. A seriação desses desenhos mostra como a Reforma Pombalina recebeu um incremento no impacto urbano e na escala das suas arquiteturas durante esse tempo, em particular na definição de estabelecimentos como o Observatório Astronómico e o Laboratório Chimico. Esse incremento deveu- -se, em parte, ao desenvolvimento natural das propostas, mas também, e em grande medida, ao competente desempenho de Elsden e ao crescente entusiasmo do próprio Marquês de Pombal em relação aos novos projetos.

Synergic Use of Multi-Sensor Satellite Data for Volcanic Hazards Monitoring: The Fogo (Cape Verde) 2014–2015 Effusive Eruption

Monitoring and retrieving information of volcanic eruptions are important tasks for assessing the hazard and its evolution in time. Satellite remote sensing data are nowadays suitable tools to perform such tasks, thanks to their capability to access disastrous event also in remote and under-monitored regions, with frequent revisit time and accurate spatial information. In this work, we have analyzed satellite images, coming from both Synthetic Aperture Radar (SAR) and Optical sensors, to characterize the 2014-2015 eruption of Fogo volcano, Cape Verde. In particular, we have exploited images collected by the European Space Agency (ESA) Sentinel-1, the Italian Space Agency (ASI) COSMO-SkyMed, and NASA/USGS Landsat-8 and Earth-Observing-1 missions, for studying the lava emplacement and volcanic source of the eruption that took place between November 2014 and January 2015. On one side, we have adopted a new automatic change detection technique for estimating the lava field and its temporal evolution, taking advantage of the intensity and the Interferometric SAR coherence. The two SAR-based features were combined using an innovative algorithm able to take full advantage of the Sentinel-1 mission’s six-day repeat cycle, thereby providing an unprecedented possibility to fully exploit the multi-temporal InSAR coherence to detect surface changes. On the other side, we have exploited the consolidated differential SAR interferometry technique to map the ground deformation and retrieve the feeding dyke by inverting syn-eruptive data. The proposed methods based on change detection for the estimation of the lava flow is capable of resolving with spatial and temporal detail the evolution of lava flows. Results from source modelling from the SAR data show a SW-NE oriented dyke, located inside Cha das Caldeiras, SW of the Pico do Fogo. The work suggests a multidisciplinary and multi-sensor approach, highlighting the benefits and limitations of satellite data and image processing techniques in an operational environment.

Caldera or flank collapse in the Fogo volcano? What age? Consequences for risk assessment in volcanic islands

The target of this study is the Fogo Island in Cape Verde, where the hazards (caldera and/or flank collapse) and the timing (120 ka or younger?) are still controversial. Using high-resolution DEM, field geological and structural analysis, and high-precision K-Ar dating, we produced an age-calibrated volcanic stratigraphy of Fogo’s summit (Chã das Caldeiras, for the last ca. 220 ka). From this, we infer the following evolution and associated processes: (1) the Fogo Volcano formed during seven stages of construction and partial destruction; (2) three flank collapses can be recognised, the biggest of which occurred between 60 and 43 ka; (3) this collapse occurred retrogressively, producing at least two distinct collapse blocks; (4) the innermost collapse was only partial, forming a flat step where a new volcano (Pico do Fogo) grew and formed the Chã das Caldeiras (literally Flat of the Calderas); (5) the removal of the buttressing eastern flank by the outermost collapse can be responsible for the seemingly “caldera” structure; (6) the growing load of the young volcano can produce a new flank failure following the innermost fault; (7) the young and closely spaced collapse ages here reported indicate a significant risk for the inhabitants of Fogo, in particular, and for the whole Cape Verde archipelago (and Atlantic seaboard) if a tsunami is produced by a future catastrophic flank collapse.

A integração das actividades turísticas nas estratégias familiares da Chã das Caldeiras, Ilha do Fogo (Cabo Verde)

The main objective of this article is to analyse the tourist activities developed in Cha das Caldeiras and how they have been incorporated into the diversity and flexibility of the family strategies that define the local domestic mode of production. The case presented here considers that the incorporation of tourism activities with those already existing is due to the type of tourism that developed in the Cha das Caldeiras, mostly exogenous factors, but also by the intrinsic aspects of the existing domestic organization, which in terms of the productive activities in rural areas, are conditioned by the uncertain economy.

Damage from lava flows: insights from the 2014\u20132015 eruption of Fogo, Cape Verde

Fast-moving lava flows during the 2014–2015 eruption of Fogo volcano in Cape Verde engulfed 75% (n = 260) of buildings within three villages in the Chã das Caldeiras area, as well as 25% of cultivable agricultural land, water storage facilities and the only road into the area. The eruption had a catastrophic impact for the close-knit communities of Chã, destroying much of their property, land and livelihoods. Volcanic risk assessment typically assumes that any object - be it a building, infrastructure or agriculture - in the path of a lava flow will be completely destroyed. Vulnerability or fragility functions for areas impacted by lava flows are thus binary: no damage in the absence of lava and complete destruction in the presence of lava. A pre-eruption field assessment of the vulnerability of buildings, infrastructure and agriculture on Fogo to the range of volcanic hazards was carried out in 2010. Many of the areas assessed were subsequently impacted by the 2014–2015 eruption and, shortly after the eruption ended, we carried out a post-eruption field assessment of the damage caused by the lava flows. In this paper, we present our findings from the damage assessment in the context of building and infrastructural vulnerability to lava flows. We found that a binary vulnerability function for lava flow impact was appropriate for most combinations of lava flow hazard and asset characteristics but that building and infrastructure type, and the flow thickness, affected the level of impact. Drawing on these observations, we have considered potential strategies for reducing physical vulnerability to lava flow impact, with a focus on buildings housing critical infrastructure. Damage assessments for lava flows are rare, and the findings and analysis presented here are important for understanding future hazard and reconstruction on Fogo and elsewhere.

Volcanic Conduits of the Chã das Caldeiras Caldera (Fogo Island, Cape Verde) – REE and Fe Crystalchemistry

Topsoils of pyroclastic materials collected on two volcanic conduits of the Chã das Caldeiras caldera of the oceanic Fogo Island (Cape Verde) were studied. Significant positive Eu anomalies were found in both pre-historic and historic cones, which together with the presence of jarosite, may be considered hydrothermal signatures that survived in this surficial semi-arid environment.

Volcanic and structural evolution of Pico do Fogo, Cape Verde

In recent months the media have drawn attention to the Cape Verde archipelago, with particular focus on the island of Fogo, the only island presently active and with an eruption that began on 23 November 2014, finally ceasing on 7 February 2015. The Monte Amarelo conical shield forms most of the 476 km2 almost circular island of Fogo. After attaining a critical elevation of about 3500 m, the Monte Amarelo shield volcano was decapitated by a giant landslide that formed a caldera‐like depression (Cha das Caldeiras), which was subsequently partially filled by basaltic nested volcanism. This younger eruptive activity culminated in the construction of the 2829 m‐high Pico do Fogo stratocone, apparently entirely made of layers of basaltic lapilli. Continued growth of the Pico do Fogo summit eruptions was interrupted in 1750, most likely after the stratocone reached a critical height. Since then, at least eight eruptions have taken place inside the landslide depression at the periphery of the Pico do Fogo cone, including the 2014–2015 eruptive event. Strong geological similarities with the Canary Islands, 1400 km to the north, have been frequently noted, probably as a consequence of a common process of origin and evolution associated with a mantle hot‐spot. These similarities are particularly evident when comparing Fogo with the Teide Volcanic Complex on Tenerife, where a lateral collapse of the Las Cañadas stratovolcano also formed a large depression (the Caldera de Las Cañadas), now partially filled with the 3718 m‐high Teide stratocone. However, important geological differences also exist and probably relate to the contrasting evolutionary stages of both islands. The Las Cañadas volcano on Tenerife formed at a late post‐erosional stage, with predominantly evolved (trachyte and phonolite) magmas, while at Fogo basaltic volcanism is still dominant.

Reducing volcanic risk on Fogo Volcano, Cape Verde, through a participatory approach: which outcome?

Abstract. This research paper presents the outcomes of Work Package 5 (socio-economical vulnerability assessment and community-based disaster risk reduction) of the MIAVITA (MItigate and Assess risk from Volcanic Impact on Terrain and human Activities) research programme conducted on Fogo Volcano, Cape Verde. The study lasted for almost 3 years (May 2010 to January 2012), of which most of the time was spent in the village of Chã das Caldeiras, situated within the 9 km wide caldera of the volcano inside Fogo Natural Park. The objectives of the programme included assessment of the vulnerability of the community at risk in terms of livelihoods, access to resources, and power relations between the local people and the different public and private institutions. These are important factors that need to be investigated in order to understand the root causes of vulnerability of the local people. This case study shows that the voluntary exposure of people to volcanic threats is linked to daily access to sources of livelihood, especially agriculture and tourism. This is despite the perception of people of the risk to their lives and properties. In order to counter the factors of vulnerability, the study also aimed to identify and enhance local capacities. To achieve such an objective, a participatory three-dimensional mapping (P3DM) activity was conducted to facilitate the dialogue between the local people and the different stakeholders as well as to prepare plans and measures to reduce volcanic risk. The P3DM was a half success considering that it has not yet led to an operational plan which takes into account the local capacities. The main reasons included (1) the non-participatory aspect of the project at the beginning which should have identified priorities for people and let them lead the project to ensure the sustainability of (2) deep conflicts within the community which complicated the focus group discussions around the 3-D map, and the difficulties in involving more marginalised people like women and the youth, and (3) the fact that volcanic risk is not a priority for the people, who are more concerned with daily difficulties due to unsustainable livelihoods, a lack of access to water, land tenure, and the restrictions by the Fogo Natural Park administration and the municipal officials. Still, the study was successful in creating a space for dialogue between the local people and the outside stakeholders such as the Natural Park Administration, the Civil Protection, and the Municipality of Santa Catarina, who have all participated actively during the course of the project.

Breve notícia da recente erupção na ilha do Fogo e suas consequências

BRIEF NOTES ABOUT THE RECENT VOLCANIC ERUPTION AT FOGO ISLAND - This article provides a concise description of the volcanic eruption that occurred in 1995 in the island of Fogo (Cape Verde). It focuses on the evolution of the eruption, its characteristics, and the alteration it produced on the topography and morphology of the landscape of Chã das Caldeiras. The consequences of this phenomenon on the human and agricultural occupation are also emphasized.

Barometry of lavas from the 1951 eruption of Fogo, Cape Verde Islands: Implications for historic and prehistoric magma plumbing systems

Fogo is one of the most active oceanic volcanoes in the world. The island was affected by a prehistoric giant lateral collapse that decapitated the summit of the former Monte Amarelo volcano. Subsequent volcanism has partly filled the collapse scar and built up the present-day Cha das Caldeiras plain and the Pico do Fogo stratovolcano. We have conducted a thermobarometric study of historic and prehistoric, basanitic to tephritic rocks in order to gain insight into Fogo's magma plumbing system and the impact of the collapse event on fractionation depths. A main focus was the penultimate 1951 eruption, which produced basanites to tephrites (5.0–8.2wt.% MgO) at two sites south and northwest of Pico do Fogo. Clinopyroxene–melt barometry of phenocrysts yields a well-confined pressure range of 480–650MPa for the final crystallization level. Microthermometric data of CO2-dominated fluid inclusions in olivine and clinopyroxene phenocrysts yield systematically lower pressures of 250–430MPa. Inclusions in cumulate xenoliths yield pressures of 100–290MPa. The combined data indicate pre-eruptive magma storage in the uppermost mantle between 17 and 22km depth and syn-eruptive short-term magma stalling within the lower crust at 8–13km depth. The lower pressures revealed by fluid inclusions in xenoliths may indicate that they originate from pre-1951 magma pulses that stalled and crystallized at variable levels in the crust. There is, however, no petrologic evidence for persistent crustal magma chambers. Clinopyroxene–melt barometric data of other historic and prehistoric eruptions indicate that magma storage and differentiation occurred in the uppermost mantle at pressures between 420 and 870MPa (15–30km depth) throughout the subaerial evolution of Fogo. Our data indicate that fractionation depths decreased significantly during a period of about 100ka representing a strong growth phase of Fogo edifice leading up to the giant Monte Amarelo flank collapse at 123–62ka. This trend seems to have been interrupted by the flank collapse, as early post-collapse magmas stagnated at deeper levels than late pre-collapse ones. Historic eruptions show shallower and broader pressure ranges, indicating an increase in complexity of the magma storage systems. Thus petrologic data indicate that flank collapse events may significantly influence deep-seated magma plumbing systems beneath ocean islands.

Utilização do Quociente de de Liocourt na avaliação da distribuição diamétrica em fragmentos de Floresta Ombrófila Aberta em Pernambuco.

Grande parte da biodiversidade do ecossistema das florestas tropicais está se perdendo, antes mesmo que se tenha inteiro conhecimento de sua riqueza natural, assim, torna-se importante a realização de estudos, a fim de propiciar o conhecimento e a manutenção da sua estrutura, além de viabilizar a exploração de seus produtos, bens e/ou serviços provenientes de forma planejada e racional, garantindo o fluxo contínuo desses recursos. Dessa forma, o objetivo deste trabalho foi utilizar o quociente de De Liocourt na avaliação da distribuição diamétrica em fragmentos de Floresta Ombrófila localizados no município de Catende, Zona da Mata Sul do estado de Pernambuco, visando a descrever a estrutura diamétrica dos fragmentos estudados pelo seu Índice de Valor de Importância (IVI), bem como avaliar a degradação e o estado sucessional das áreas. A distribuição diamétrica comportou-se como o esperado para florestas inequiâneas, ou seja, curva de distribuição diamétrica assemelhando-se a um J-invertido. Os valores de área basal nos fragmentos foram de 23,6m2.ha-1, para a Mata das Caldeiras e de 20,9 m2.ha-1 para a Mata das Galinhas. Os fragmentos pesquisados encontram-se em estágio médio de sucessão. Algumas espécies apresentaram dificuldades na taxa de recrutamento, podendo gerar futuramente a sua extinção. Espécies como: Tapirira guianensis Aubl., Dialium guianense (Aubl.) Sandwith e Brosimum discolor Schott, demonstraram estrutura diamétrica distinta entre os fragmentos. A espécie Plathymenia foliolosa Benth. apresentou descontinuidade acentuada na estrutura diamétrica em ambas as áreas.

Estrutura diamétrica de um fragmento de Floresta Atlântica em matriz de cana-de-açúcar, Catende, Pernambuco

Objetivou-se, neste trabalho, analisar a estrutura diamétrica do componente arbóreo de um fragmento de Floresta Atlântica inserido em uma matriz de cana-de-açúcar, utilizando-se o quociente "q" de De Liocourt. O estudo foi realizado no fragmento denominado Mata das Caldeiras, no município de Catende, Pernambuco. Os indivíduos amostrados foram distribuídos em classes de diâmetro com amplitude de 5 cm, em que o centro da primeira classe tem o valor de 6,5 cm. Com o uso do quociente "q" de De Liocourt, aqui empregado, construíram-se as curvas de distribuição diamétrica, observadas e estimadas para a amostragem geral e para as espécies de maior Valor de Importância (VI). O fragmento Mata das Caldeiras apresentou déficit de árvores nas classes de diâmetro, geral e por espécies de maior VI, comparado a uma floresta balanceada. O quociente "q" de De Liocourt pode ser usado para avaliar estrutura diamétrica em fragmentos de Floresta Atlântica. Por meio da distribuição diamétrica e dos valores de "q" obtidos para o estágio de sucessão em que se encontram as áreas, pode-se inferir que o grau de perturbação nesses fragmentos ocorre de forma constante.

InSAR observations of the 1995 Fogo, Cape Verde, eruption: Implications for the effects of collapse events upon island volcanoes

Fogo volcano, Cape Verde Islands, erupted in April 1995 after 43 years of dormancy. About 46 106 m3 of lava erupted during 7.5 weeks from vents on the SW flank of Pico do Fogo into Cha das Caldeiras. Interferograms obtained from 1993–1998 ERS SAR data show ground deformation due to the feeder dike but lack evidence for any volcano‐wide deformation related to volume changes of a shallow magma reservoir. This suggests that Fogo is fed from a relatively deep, mantle‐lithospheric source (>16.5 km depth), consistent with petrological data. This supports the concept that Cha das Caldeiras is the fill of a collapse scar created by a giant landslide, and not a collapse caldera overlying a central, shallow magma chamber. The disturbance of the magmatic system by giant landslides may explain why some oceanic island volcanoes with high magma supply rates currently lack well‐developed shallow reservoirs.

Comparison and cross-checking of historical, archaeological and geological evidence for the location and type of historical and sub-historical eruptions of multiple-vent oceanic island volcanoes

Abstract Oceanic island volcanoes, like many others, have many small vents scattered over their flanks in addition to, or in place of, large summit vents. These small vents are commonly monogenetic and many eruptions of this type of volcano involve activity at more than one such vent: lines of volcanic cones are often produced by eruptions fed by dykes, and if more than one dyke is emplaced during an eruption these vents can be along different alignments, and many kilometres apart. Identifying which vents were produced in which eruptions is an important problem in reconstructing the development of multiplevent volcanoes. Reconstruction of historical and sub-historical eruptions of two oceanic island volcanoes, the Cumbre Vieja volcano on La Palma in the Canary Islands and Cha das Caldeiras volcano on Fogo, Cape Verde Islands, has indicated that historical eyewitness accounts and archaeological evidence can be extremely valuable adjuncts to detailed geological studies. In contrast, secondary accounts including folk memories and earlier accounts in the scientific literature are commonly inconsistent both with the eyewitness accounts and with the results of detailed geological mapping, archaeological evidence or other historical documents. A common source of error is confusion of the vents of historical eruptions with older but larger or more prominent volcanic vents that lie along the same line of sight as viewed from adjacent settlements or from convenient viewpoints. Examples of this are provided by mis-locations of the vents of the AD 1677 eruption on La Palma and of some of the vents of the AD 1951 eruption on Fogo. Another problem arises when the location or style of eruption on a volcano has changed in early historical time, as has occurred on Fogo. The differences between early historical accounts of eruptions on this volcano and the more detailed accounts of more recent eruptions has led to the discrediting of the former by some researchers, whereas geological studies have supported the early historical accounts.

A past giant lateral collapse and present-day flank instability of Fogo, Cape Verde Islands

Fogo island is a large and extremely steepsided oceanic island volcano in the Cape Verde archipelago. It has a large (ca. 9 km across) east facing summit collapse structure, the Monte Amarelo collapse, with a probable volume of at least 150–200 km3. For most of its history the Monte Amarelo volcano had a small but productive central vent complex and radial rift zones fed by laterally propagating dykes. Shortly before the collapse the latter were replaced by north–south-trending arrays of en echelon, vertically propagating dykes. Since the Monte Amarelo collapse the scar has partly filled with a new volcano, the Cha das Caldeiras volcano. The summit cone of this volcano, the Pico do Fogo, is a very young feature but has been abandoned in the most recent phase of activity, from the 18th century onwards. The same period has also seen the abandonment of earlier radial rift zones with laterally propagating dykes and their replacement with en echelon arrays of vents fed by vertically propagating dykes. These form an N–S-trending array within the older collapse structure and are associated with seaward displacement of the eastern flank of the volcano within the old collapse structure. The most recent eruptions, those of 1951 and 1995, appear to be associated with episodes of flank instability manifested in N–S surface fissuring and east facing normal faults. These recent structural changes in the volcano parallel those which took place in the Monte Amarelo volcano prior to its collapse.